Determining return of spontaneous circulation during cpr

ABSTRACT

A device for supporting determination of return of spontaneous circulation, ROSC, during an associated cardiopulmonary resuscitation, CPR, procedure which is being performed on an associated patient. A sensor is used to sense a physiological signal of the patient. Frequency analysis of the signal is carried out to extract dominant fundamental frequency components in the signal. From this analysis it is possible to determine that there has been a potential ROSC.

FIELD OF THE INVENTION

The present invention relates to the field of determining return ofspontaneous circulation, in particular the invention relates to adevice, method and computer program for supporting the determination ofreturn of spontaneous circulation during cardiopulmonary resuscitation.

BACKGROUND OF THE INVENTION

Cardiopulmonary resuscitation for cardiac-arrest patients is anemergency procedure with a very low survival rate (5-10%). It iscommonly accepted that the quality of the chest compressions is ofcrucial importance for successful defibrillation and outcome.

Detecting return of spontaneous circulation (ROSC) duringcardiopulmonary resuscitation (CPR) is challenging. Typically, ROSCdetection involves manual palpation for an arterial pulse, for exampleat the neck of the patient. Manual palpation requires interrupting thechest compressions and is known to be time-consuming, which cantherefore lead to reduced blood flow and a reduced chance of ROSC.

To minimize the duration of this type of pause, clinical guidelinesstate that a pulse-check pause should take no longer than 10 seconds. Inclinical practice, manual pulse checks often take much longer than 10seconds and are known to be unreliable even if performed by expertclinicians.

Alternatively, a reliable and objective measurement to support ROSCdetection is an arterial blood pressure measurement, which can beinterpreted to indicate ROSC when the systolic blood pressure is higherthan, e.g., 60 mmHg. However, this is an invasive measurement whichrequires placement of catheters and is consequently not alwaysavailable. Therefore, a non-invasive method that can support ROSCdetection during ongoing chest compressions would be a valuable asset.

The reference US 2012/0035485A1 describes that the presence of a cardiacpulse in a patient may be determined by evaluating physiological signalsin the patient. In one embodiment, a medical device evaluates opticalcharacteristics of light transmitted into a patient to ascertainphysiological signals, such as pulsatile changes in general blood volumeproximate a light detector module. Using these features, the medicaldevice determines whether a cardiac pulse is present in the patient. Themedical device may also be configured to report whether the patient isin a VF, VT, asystole, or PEA condition, in addition to being in apulseless condition, and prompt different therapies, such as chestcompressions, rescue breathing, defibrillation, and PEA-specificelectrotherapy, depending on the analysis of the physiological signals.Auto-capture of a cardiac pulse using pacing stimuli is furtherprovided.

Reference R.W.C.G.R. et Al: “Detection of a spontaneous pulse inphotoplethysmograms during automated cardiopulmonary resuscitation in aporcine model”, RESUSCITATION, vol. 84, 2013, pages 1625-32, XP55125349discloses an investigation of the potential of photoplethysmography(PPG) signals to detect the presence and rate of a spontaneous cardiacpulse during CPR, by retrospectively analyzing PPG and arterial bloodpressure signals simultaneously recorded in pigs undergoing automatedCPR.

EP 2 883 493 discloses a system for real-time recognition of restorationof spontaneous circulation which uses time-domain and frequency-domainrecognition logic. US 2013/0338724 discloses a system which uses two ormore physiological signals to detect a cardiac pulse.

Thus, there have been various attempts to monitor physiological signalsto detect the presence of a spontaneous pulse. Monitoring of end-tidalCO2, invasive blood pressure, or central venous oxygen saturation,allows for an objective assessment of pulse, but requires a securedairway or placement of catheters. Trans-thoracic impedance (TTI)measurements, and near-infrared spectroscopy (NIRS) are non-invasive,but TTI is strongly influenced by chest compressions and NIRS respondsslowly upon ROSC.

While analysis of photoplethysmography data for pulse detection has beenproposed, the data is not easy to interpret.

There remains a need for a reliable way to detect ROSC in a non-invasiveway and without interrupting the chest compression sequence beingperformed on an associated patient. In particular, there is a need for afast, automated, and accurate method to do a pulse check which givessimple to interpret results, so as to reduce the duration of any pausesand to reduce the amount of false pulse determinations. Recording of theelectrocardiogram (ECG) alone does not provide the information as theheart may be electrically active but may not produce cardiac output.

SUMMARY OF THE INVENTION

Examples in accordance with a first aspect of the invention provide adevice for supporting determination of return of spontaneouscirculation, ROSC, during an associated cardiopulmonary resuscitation,CPR, procedure which is being performed on an associated patient, thedevice comprising:

-   -   an input for receiving a signal from a sensor for sensing a        physiological signal of the patient;    -   a processor, which is adapted to:        -   perform frequency analysis of the physiological signal;        -   detect and discriminate compression-induced components and            spontaneous pulse components within the physiological            signal;        -   provide an output based on the detected components within            the physiological signal to support determination that there            has been ROSC; and    -   a display device,    -   wherein the processor is adapted to control the display device        to output an image which shows the compression-induced        components and spontaneous pulse components within the        physiological signal, over time as a frequency-time plot.

This invention is based on a frequency analysis of a physiologicalsignal, such as a photoplethysmography (PPG) signal and/or anelectrocardiography (ECG) signal acquired during CPR. By analyzing aphysiological signal to extract the compression-induced components andthe spontaneous pulse components, information about the CPR as well asany spontaneous pulse may be provided to a clinician, to assist them indetermining that there has been ROSC.

The image output may for example involve displaying the dominantfrequency components in the sensor signal. These dominant frequencycomponents may be shown as they evolve over time.

Such a time-frequency representation can simultaneously provide visualfeedback on the rate at which the chest compressions are delivered(which can be used to assess CPR quality), and the absence or presenceof an underlying spontaneous pulse based on the physiological signal(PPG and/or ECG). Feedback on the absence or presence of an underlyingspontaneous pulse, and the CPR feedback, may then be provided duringongoing chest compressions.

The displayed information may comprise a first trace which visuallyprovides feedback about the rate at which the chest compressions aredelivered over time throughout the CPR event. Feedback on chestcompression rate can support the caregiver to deliver chest compressionsat a rate of 100-120 per minute as advised in CPR guidelines.

If a heart rate is detected in an ECG signal or an underlyingspontaneous pulse is detected in a PPG signal during CPR, this can beshown in the time-frequency representation by using an additional tracedifferent from the trace indicating the chest compression rate overtime. Specifically, the time-frequency representation may then show thehistory of the chest compression rate delivered throughout the CPR eventas well, which serves as a reference to facilitate recognizing theappearance of the traces indicating the heart rate and the spontaneouspulse rate.

Simultaneously showing the heart rate (i.e. electrical heart activity)and the pulse rate (a perfusing heart rhythm) in a single time-frequencyrepresentation furthermore facilitates determining whether each R peakin the ECG leads to a contraction of the heart.

In one example, the processor is adapted to extract dominant fundamentalfrequency components of harmonic frequency series within thephysiological signal and provide an output based on the extracteddominant fundamental frequency components to support determination thatthere has been ROSC.

By extracting the dominant fundamental frequency components, easy tointerpret information may be provided to the clinician. The analysis mayalso enable determination of a potential ROSC automatically. Theautomatic determination of a potential ROSC may however be based on theanalysis of the full harmonic series. This automatic determination of apotential ROSC may be used by a clinician as further guidance, ratherthan providing an absolute indication of ROSC. Note that determiningwhether a patient has ROSC is a clinical, situational assessment. It notonly involves determining whether there is a spontaneous pulse, but italso involves determining whether the output (blood flow) generated bythe heart is life-sustaining. This is an assessment which only can bemade by a medical doctor, as the cardiac output needed to stay alivevaries from one patient to the other and even varies over time withinone patient. The monitoring equipment supports the clinician indetermining whether there is ROSC by showing information derived frommeasurements.

The output signal provides information automatically about ROSC and canbe used to avoid the need to take pulse checks during CPR if there is nospontaneous pulse. The output can guide the clinician as to when pulsechecks should be taken, or when administration of vasopressors isappropriate. A frequency analysis representation of the PPG signal canobjectively show whether an underlying spontaneous pulse is presentduring CPR. Unnecessary interruptions in chest compressions for lengthyand futile pulse checks can be prevented in case of pulse absence, whichcan improve CPR outcome. Vasopressors may have detrimental effects oncardiovascular stability if administered just after the heart hasstarted beating again. The system can thus be used to preventadministration of vasopressors when these may have detrimental effects,by advising a clinician during ongoing compressions whether aspontaneous pulse is present.

The processor is for example adapted to perform frequency analysis of atleast the fundamental frequency components and the first harmoniccomponents present in the physiological signal.

By analyzing multiple frequency components, it is possible todistinguish more reliably between a pulse induced by the CPR and aspontaneous pulse. In particular, differences may be greater between thehigher harmonic frequency components than the fundamental frequencycomponents. Frequency analysis may be carried out of at least the secondharmonic components present in the physiological signal.

The sensor for example may comprise an ECG sensor and/or a PPG sensor.

A second sensor or sensors may also be provided for sensing the CPRcompressions and/or a capnography signal (which measures concentrationor partial pressure of CO2). A CPR sensor can be used to give aclinician feedback about the quality of CPR being delivered, such as thecompression depth and the compression rate. A capnography signal sensormay be used to assist in more reliable interpretation of thephysiological sensor e.g. PPG signal. This provides a means to betterassess the adequacy/quality of a spontaneous pulse component in a PPGsignal.

The processor is thus preferably adapted to determine the quality of anydetermined ROSC. This may be based on a signal to noise analysis of thespontaneous pulse signal, or an energy measurement of the spontaneouspulse signal. Thus, the processor may be adapted to control the displaydevice to output an image which shows:

-   -   the quality of the CPR compressions; and/or    -   the quality of any determined ROSC.

Examples in accordance with another aspect of the invention provide amethod for supporting determination of return of spontaneouscirculation, ROSC, during an associated cardiopulmonary resuscitation,CPR, procedure which is being performed on an associated patient, themethod comprising:

-   -   sensing a physiological signal of the patient;    -   performing frequency analysis the physiological signal;    -   detecting and discriminating compression-induced components and        spontaneous pulse components within the physiological signal;        and    -   providing an output on a display device based on the detected        components within the physiological signal to support        determination that there has been ROSC, wherein the output shows        the compression-induced components and spontaneous pulse        components within the physiological signal over time as a        frequency-time plot.

This method provides support to a clinician to support determination ofROSC. It may provide automatic recognition of a potential ROSC duringCPR.

The determined recognition of a potential ROSC is for example displayedto a user.

The frequency analysis may involve extracting dominant fundamentalfrequency components of harmonic frequency series within thephysiological signal. The extracted dominant fundamental frequencycomponents are preferably also displayed in the form of a frequencyversus time plot.

As explained above, the frequency analysis may be performed on at leastthe fundamental frequency components and the first harmonic componentspresent in the physiological signal, and optionally also at least thesecond harmonic components present in the physiological signal.

The method may further comprise sensing the CPR compressions anddetermining the quality of the CPR compressions.

The method preferably also comprises outputting an image on a displaydevice, which image shows:

-   -   the quality of the CPR compressions; and/or    -   the quality of any determined potential ROSC.

This information is preferably shown over time so that the evolution ofthe signals can be seen.

The invention also provides a computer program (and a computer programcarrier) for implementing the method defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the drawings, in which:

FIG. 1 shows a first example of a patient monitoring system inaccordance with the invention;

FIG. 2 shows a first example of possible display output;

FIG. 3 shows a second example of possible display output;

FIG. 4 shows a third example of possible display output;

FIG. 5 shows a fourth example of possible display output;

FIG. 6 shows further display output traces that may be provided andshows traces for an animal patient;

FIG. 7 shows the display output traces of FIG. 6 for another CPR(animal) patient;

FIG. 8 shows the display output traces of FIG. 6 for yet another CPR(animal) patient; and

FIG. 9 shows a second example of a patient monitoring system inaccordance with the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides a device for supporting determination of returnof spontaneous circulation, ROSC, during an associated cardiopulmonaryresuscitation, CPR, procedure which is being performed on an associatedpatient. A sensor is used to sense a physiological signal of thepatient. Frequency analysis of the signal is carried out, for example todetect dominant frequency components in the signal. From this analysisit is possible to support determination that there has been ROSC bypreparing an output for a clinician which enables easy and rapid furtherinterpretation.

FIG. 1 shows a system 110 comprising a device 100 for supportingdetermination of return of spontaneous circulation, ROSC, during anassociated cardiopulmonary resuscitation, CPR, procedure. The device 100functions as a patient monitor. In this example, it also functions as adefibrillation device in the sense that it comprises electronics 114 forcontrolling defibrillator pads 106.

The device receives an input from a physiological sensor 102, which maybe a commercial PPG sensor or an ECG monitor. The device 100 contains acontroller 112 with access to or comprising one or more predeterminedalgorithms.

The system also comprises a display 116.

The device is connected to a defibrillator, such as a set ofdefibrillator pads 106. This allows the algorithm to know when the shockis given and to obtain information on the chest compressions via, e.g.,a transthoracic impedance measurement.

The device may be used for monitoring a patient during manual CPR, butit may also be used with an automated CPR device.

A second input to the device 100 receives a sensor signal from a CPRmonitor such 104 such as an accelerometer. This provides informationconcerning CPR compression frequency, phase, and acceleration, velocityand depth as well as compression pauses.

In alternative embodiments, the system does not comprise thedefibrillator pads 106 and/or the automated CPR device and/or theaccelerometer 104.

The controller performs frequency analysis of the sensed physiologicalsignal. In one set of examples, it extracts dominant fundamentalfrequency components of the physiological signal. An output is providedto the display based on the frequency analysis, for example based on theextracted dominant fundamental frequency components, to support theclinician to determine that there has been ROSC.

FIG. 2 shows a first example of possible display output.

The output is in the form of a time-frequency representation showing thefundamental compression rate (line 200), arrhythmic spontaneous pulses(dots 202) and the stable fundamental spontaneous pulse rate (line 204).The pulses 202 occur when the heart restarts beating again.

The lines may have a width which represents how variable the frequencyis, so the wider the line, the more variable the frequency is. This isnot shown.

A timer 206 indicates the duration of the period that a stablespontaneous pulse has been detected uninterruptedly.

The time-frequency representation in FIG. 2 shows a 5 minute episode ofCPR. The x-axis shows time in minutes:seconds, starting at 9 minutes(after an arbitrary starting point) and ending at 14 minutes. The y-axisshows the frequency.

CPR compressions are delivered from 09:00 up to about 12:25. A stablespontaneous pulse appears at about 11:15. Between 10:30 and 11:15arrhythmic spontaneous pulses have been detected in the PPG signal, asindicated by the dots 202. As spontaneous pulses occur at irregularintervals, no pulse rate exists.

Symbols indicating the chest compression rate (hand 208) and spontaneouspulse rate (heart 210) are positioned at the most recent point of thetrace.

The history of the delivered compression rates facilitates detecting thechange in the representation occurring at 11:15. The timer 206 startsrunning from the moment that a stable spontaneous pulse rate has beendetected in the PPG signal, indicating the duration that a spontaneouspulse has been detected.

In FIG. 3 a spontaneous pulse has been detected for 02:45 minutes.Should the spontaneous pulse disappear again, then the timer willfreeze. If a stable spontaneous pulse subsequently re-appears, the timerwill start running again from 00:00.

Showing the duration that a stable spontaneous pulse has been detecteduninterruptedly supports the clinician in deciding when to interrupt thechest compressions to determine whether the spontaneous pulse ispalpable and there is ROSC.

To arrive at this time-frequency representation, the physiologicalsignal (e.g. PPG signal) is processed and analyzed in the time andfrequency domains as explained above. Time domain analysis is employedto detect the arrhythmic pulses, indicated by the dots 202. Frequencydomain analysis will provide an averaged pulse rate. Via time-domainanalysis arrhythmic beats can be detected individually, which is usedto, e.g., determine the position of the individual dots 202 in FIG. 2.

Frequency analysis is employed to identify the harmonic seriescorresponding to the chest compressions and the harmonic seriescorresponding to the spontaneous pulse rate. The frequency analysis canbe performed by Fourier analysis, autoregressive modeling or wavelets.In this way, both compression-induced components and spontaneous pulsecomponents are detected and discriminated within the physiologicalsignal. A single physiological signal is analyzed to extract thesecomponents. In the preferred example, the single signal is a PPG signal.As explained above, the system may however have multiple physiologicalsensors, and in this way the information provided to the clinician canbe further refined.

At 11:15 the algorithm has detected presence of a sufficiently strongspontaneous pulse component in the PPG signal, based for example on thesignal-to-noise ratio, the number of harmonics, or the accumulatedenergy in all the harmonics. However, only the fundamental frequenciesof these series are shown in the time-frequency representation forclarity, and higher harmonics are omitted. Also background noise presentin the signals is not shown.

The chest compression rate may be identified either by analyzing theharmonic series present in the physiological signal, or by analyzing theindependent measurement of compressions using sensor 104. The harmonicseries in the physiological signal corresponding to the compressions canbe identified by determining the number of harmonics present in thesignal or the total power in the series relative to the noise floor. Ascompressions result in steeper pulses than a cardiac contraction, theharmonic series corresponding to the compressions contains morecomponents than the harmonic series corresponding to the spontaneouspulse.

The independent measurement of compressions may be based on a sensor 104in the form of an accelerometer integrated with the physiologicalsensor, a QCPR-pad, a radar sensor, a pressure/force sensor or atrans-thoracic impedance measurement. Any other means to obtaininformation on the compression rate and/or acceleration and/or speedand/or depth and/or force and/or pressure may be used.

The heart rate may additionally be measured by an ECG sensor, and thepulse rate may then be shown in the same time-frequency representation.This facilitates determining whether each R peak in an ECG signal leadsto a contraction of the heart. Specifically detection of pulselesselectrical activity (PEA) can be readily done, when an ECG-based heartrate (i.e. electrical heart activity but not a perfusing pulse) ispresent in the time-frequency representation, but simultaneously nospontaneous pulse rate (i.e. a perfusing pulse) can be detected in thePPG signal.

In FIG. 2, the fundamental frequency components of the chest compressionrate and the spontaneous pulse rate are shown in one time-frequencyrepresentation. In another embodiment, two time-frequencyrepresentations can be shown, one providing feedback on the rate atwhich the chest compressions are being delivered, and one providingfeedback on presence or absence of an underlying spontaneous pulse.

The time-frequency representation can be shown on the monitoring device100, for example the display of a monitor-defibrillator, or the displayof an automated external defibrillator (AED).

Additionally, the monitoring device 100 may wirelessly communicate thetime-frequency representation to a separate device that serves as adisplay only, for example a smartphone or a tablet, which can bepositioned next to the victim so it is easily observed by the caregiverwhile delivering chest compressions and ventilations. A headset device(such as Google glass) may also be used to display information to theuser, while enabling them to continue concentrating on the task they areperforming.

The required physiological sensor can be a PPG sensor, eithertransmissive or reflective, or a non-contact sensing means such as acamera. This sensor can also be an ECG measurement using one or moreleads. These may form part of the defibrillator pads.

One suitable system for obtaining PPG (pulse oximetry) data includes asensor with a red LED, a near-infrared LED, and a photodetector diode,where the sensor is configured to place the LEDs and photodetector diodedirectly on the skin of the patient, typically on a digit (finger ortoe) or earlobe. Other places on the patient may also be suitable,including the forehead, the nose or other parts of the face, the wrist,the chest, the nasal septum, the alar wings, the ear canal, and/or theinside of the mouth, such as the cheek or the tongue. The LEDs emitlight at different wavelengths, which light is diffused through thevascular bed of the patient's skin and received by the photodetectordiode. The resulting PPG signal may then be analyzed for one or morefeatures indicative of a cardiac pulse. Other simpler versions of asystem for obtaining PPG data may be used, including a version with asingle light source of one, e.g., green, or more wavelengths. Theabsorption or reflectance of the light is modulated by the pulsatilearterial blood volume and detected using a photodetector device. In anembodiment, PPG data can be obtained from camera images, where ambientlight and/or additional light sources are used to illuminate the tissue,such as skin.

PPG measurements can be carried out at a distance from the tissue, wherethe light source and/or detector are not in contact with the tissue,such as in the case of camera-based measurements. The PPG data may beobtained at one or more wavelengths, such as 1, 2, 3, 4, 5, 6, 7, 8, 9,10 or more wavelengths. In some examples, the incoming light is ambientlight, such as sunlight. In an embodiment, PPG data may be obtainedusing a pulse oximeter which monitors the perfusion of blood, such asmonitors the perfusion of blood to the dermis and subcutaneous tissue ofthe skin, and/or monitors the perfusion of blood through mucosal tissue.Apparatus and techniques for obtaining PPG data, such as pulse oximetrydata, are well known in the art.

The second sensor 104 for independently measuring characteristics of thedelivered compressions is optional. If used, it measures at least thecompression rate, but it may also include compression acceleration,speed, depth, force, and pressure.

In the physiological signal, the dominant frequency components are (1)the fundamental chest compression frequency if chest compressions arebeing delivered, and (2) the fundamental spontaneous pulse rate if theheart beats again. The dominant frequency component is the fundamentalchest compression rate if chest compressions are being delivered.

The analysis of the spectral components in the PPG/ECG and compressionsignals can be based on Fourier analysis, autoregressive modeling orwavelet analysis. To discriminate between the compression rate and thespontaneous pulse/heart rate, higher harmonics are analyzed as well,because the frequency difference between the higher harmonics is largerthan the frequency difference between the fundamental components. Thus,by analyzing the harmonics the contrast between the spontaneouspulse/heart rate and the compression rate is improved. Furthermore, theharmonic series present in the PPG/ECG signal caused by compressions canbe recognized by analyzing the harmonics in the series. Analysis of theharmonics can for instance comprise analyzing the number of harmonicsand/or analyzing the total power in the harmonic series relative to thenoise floor. In this way, the analysis of the harmonic series canobviate the need of an independent measurement of compressions.

The processing unit extracts the dominant components, i.e. fundamentalfrequency components of the physiological signal harmonic series, forsubsequent display in the time-frequency representation. For clarity,only the fundamental chest compression rate and the fundamentalspontaneous pulse rate are displayed on the screen, and higher harmonicsof the chest compression rate and the spontaneous pulse rate areomitted. In the processing, however, the (energy of the) harmonics istaken into account to identify the dominant frequencies present in thesignal.

Additionally, the processing unit may determine two quality indicators.

FIG. 3 shows a second example of display output including a firstquality indicator 220 which shows the depth of the compressions derivedfrom the compression measurement. It indicates whether the compressionare within the range prescribed by the guidelines (5-6 cm), or whetherthe compressions are too shallow (<5 cm) or too deep (>6 cm). A secondquality indicator 222 shows the strength of the spontaneous pulsecomponent in the PPG signal based for example on the signal-to-noiseratio, or the number of harmonics in the PPG signal, or the accumulatedenergy of the harmonics in the harmonic series, or the stability of thepulse rate.

In another embodiment, the indicators can be incorporated in thetime-frequency representation, via a color coding of the tracesrepresenting the fundamental compression rate and fundamentalspontaneous pulse rate over time.

The indicators are of interest because during CPR, feedback on thequality of the CPR delivered and feedback on the condition of thepatient are important. For example, delivering 100-120 compressions perminute is important to achieve high-quality CPR. The quality of CPR isassociated with the CPR outcome. Also, studies have shown that real-timefeedback devices improve the quality of CPR. Providing feedback on therate at which chest compressions are delivered during CPR assists thecaregiver in achieving the desired rate of 100-120 per minute.

The displayed information enables interruptions of chest compressions tobe minimized to perform pulse checks. Furthermore, vasopressors may havedetrimental effects on cardiovascular stability if administered justafter the heart has started beating again. Showing the caregiver duringongoing compressions whether an underlying spontaneous pulse is presentcan prevent administration of vasopressors when these may havedetrimental effects. Thus, administration of vasopressors can be guidedso that when a spontaneous pulse is present, the clinician knows thatvasopressors should not be administered.

FIG. 4 shows a third example of display output, in which the fundamentalcompression rate line 200 is segmented in order to mark the instantswhen compressions are shortly interrupted. During short interruptions,the rate at which compressions were delivered previously is maintainedin the time-frequency representation for clarity. Only when thecompression measurement indicates that compressions have been stoppedfor a longer period of time, the trace disappears from thetime-frequency representation. To determine when the chest compressionshave been interrupted, time-domain analysis is needed complementary tothe frequency analysis to determine the chest compression rate.

For example, short interruptions in the chest compressions may be shownin a lighter color of the trace. When compressions are shortlyinterrupted, e.g., when the compression sensor detects no compressionsfor a period longer than 1 second but less than 5 seconds, the rate atwhich chest compressions were delivered previously is kept in thetime-frequency representation but marked by the lighter color. Only whencompressions are interrupted for a longer period of time, e.g., when thecompression sensor detects no compressions for a period longer than 5seconds, the compression trace is removed from the time-frequencyrepresentation. This approach is of particular interest for followingthe chest compression-rate during 30:2 CPR, when compressions areinterrupted every thirty compressions to deliver two ventilations (sothat an interruption of 3-5 seconds is expected).

The PPG signal can be replaced by an ECG signal in the examples above.Alternatively, the ECG and PPG signals can be combined in a singleembodiment, to support detection of Pulseless Electrical Activity (PEA).A display output for this mode is illustrated in FIG. 5.

The fundamental compression rate is again shown as plot 200 and thefundamental spontaneous pulse rate is shown as plot 204. The fundamentalheart rate is shown as plot 230 (which may be a different color to plot204 for ease of recognition. The width of each plot may again indicatethe variability of the frequency, i.e., the wider the line, the morevariable the frequency is. The timer 206 again shows the time that aspontaneous pulse rate has been detected uninterruptedly. The new timer232 shows the duration of the period that a heart rate has been detecteduninterruptedly.

The fundamental heart rate is derived from an ECG signal.

The ECG signal shows that electrical activity of the heart resumes atabout 10:10. At that point, a heart rate has been detected in the ECGsignal, which is shown by the plot 230. A spontaneous pulse is detectedin the PPG signal at about 11:15, at which point the plot 204 appears inthe time-frequency representation.

In FIG. 5 a heart rate has been detected for 03:50 (from the start ofplot 230) and a spontaneous pulse has rate has been detected for 02:45.(from the start of plot 204). If the heart rate disappears again, bothtimers will freeze. If the spontaneous pulse rate disappears, thecorresponding timer will freeze. If the heart rate or spontaneous pulserate re-appears, the corresponding timer will start running again from00:00. Showing the duration that a heart rate and a spontaneous pulserate have been detected uninterruptedly is meant to support theclinician in deciding when to interrupt the chest compressions todetermine whether the spontaneous pulse is palpable and there is ROSC.

The time-frequency representation in FIG. 5 shows how the combination ofECG and PPG can support detection of pulseless electrical activity(PEA). Initially, between 10:10 and 11:15, the electrical activity ofthe heart does not lead to actual contractions, which clearly followsfrom the presence of a detected heart rate (plot 230) and absence of adetected pulse rate (plot 204). During this interval of PEA, the monitorclearly shows that CPR should be continued, as there is no perfusingpulse.

The term “Return of Spontaneous Circulation” (ROSC) as used in thisapplication is understood as is known in the art, and refers to Clinicalsignificance of return of pulse.

A patient can only have Return of Spontaneous Circulation (ROSC) when aperfusing and life-sustaining rhythm has been re-established, i.e., whenthe heart contracts again at a stable rate, resulting in cardiac outputwhich is adequate in providing sufficient nutrients and oxygen to thetissues to keep the person alive. Therefore, by detecting the pulserate, one may provide the clinician with information about the rate atwhich the heart contracts and pumps blood.

If this rate is too low, e.g., when the rate is below 1 Hz, theclinician can decide that there is no ROSC yet and that delivering chestcompressions should be continued. Furthermore, when the detected pulserate varies too much over time, this may indicate that the heart is notyet pumping in a stable fashion. This information can also be of use tothe clinician to help him decide how to continue the CPR process.

When the heart is pumping again at a stable rate higher than, e.g., 1Hz, the clinician can decide to further examine whether there is ROSC,by doing additional measurements (e.g., blood pressure, or end-tidalCO2). Presence of a stable pulse rate which is sufficiently hightherefore is a prerequisite of ROSC: without such a rhythm, there willbe no ROSC, and it will be of no use to do a further assessment of ROSC.On the other hand, presence of a stable, sufficiently high pulse rate ina PPG signal does not directly indicate that there is ROSC, because itdoes not provide the clinician with the information about the underlyingblood pressure and/or level of perfusion. Additional measurements arerequired to determine this. Nonetheless, via embodiments of the presentinvention one can easily, and non-invasively obtain information aboutpresence or absence of a stable, perfusing rhythm at a sufficiently highrate. Therefore, via the PPG-based pulse rate measurement, such as viaembodiments of the present invention, the clinician can decide whetheror not to stop chest compressions and do a further assessment of ROSC.

The example of FIG. 5 shows the benefit of combining information frommultiple sensor types in order to derive additional information or toenable more reliable or simpler interpretation of data.

Another approach in accordance with the invention is to combine aphotoplethysmography (PPG) signal and a capnography (CO2) signal (inparticular an end-tidal CO2, ETCO2) to provide an indicator ofcardiogenic output, which can support the clinician in detecting ROSC.In some examples, an electrocardiography (ECG) signal and a compressionreference/motion signal are included as well.

By combining PPG and ETCO2, the interpretation of ETCO2 is made morespecific. If ETCO2 increases without presence of a spontaneous pulse asdetected from the PPG signal, it can be concluded that the increase inETCO2 is not caused by spontaneous cardiac contractions. On the otherhand, if the PPG signal shows presence of a spontaneous pulse, the ETCO2signal can indicate the adequacy of the perfusion resulting fromspontaneous cardiac contractions. Furthermore, the PPG signal providesthe spontaneous pulse rate as explained above, which cannot be obtainedfrom the ETCO2 signal, and PPG can show presence of a spontaneous pulseearlier than ETCO2. By combining PPG and ETCO2 a more reliable indicatorof cardiogenic output is obtained compared to using either of thesignals separately.

The additional information derived from the ETCO2 signal can thus bedisplayed to further guide the clinician during CPR. Although PPG can beused to detect the onset of pulses, it does not provide a measure ofperfusion. Furthermore, PPG can detect presence of spontaneous pulses atsub-life-supporting blood pressures.

Currently, CPR guidelines state that capnography can be used to obtainan indication of return of spontaneous circulation (ROSC). Theguidelines state that an end-tidal CO2 (ETCO2) level exceeding 40 mmHgcan be considered indicative of ROSC. However, the disadvantages ofETCO2 alone are:

-   -   the response in ETCO2 when the heart resumes output may be        relatively slow, taking approximately 0.5-2 min before reaching        an ETCO2 level of about 30-40 mmHg.    -   interpretation of the actual level can be complicated and there        is no clear cutoff between ROSC and no ROSC.    -   CO2 does not provide information on the spontaneous pulse rate.

By combining a PPG signal with an ETCO2 signal a stronger indication ofa potential return of spontaneous circulation (ROSC) is provided. ROSCmeans a resumption of sustained and life-sustaining perfusing cardiacactivity associated with significant respiratory effort after cardiacarrest. Here, a sudden and sustained increase in ETCO2 is interpreted asan indicator of perfusion, when the PPG signal shows presence of aspontaneous pulse. Furthermore, the interpretation of the ETCO2 level ismore specific by the combination with a spontaneous pulse in the PPGsignal.

If the PPG signal does not indicate a spontaneous pulse, a high ETCO2level may be caused by for example hypoventilation. By taking intoaccount ETCO2, a measure of circulation can be obtained which is usefulto assess whether the level of circulation can be life-sustaining, whichin turn can support the detection of ROSC.

The advantage of combining PPG and ETCO2 is described by FIGS. 6 to 8.They show measurement results obtained from pigs undergoing automatedCPR with a protocol of thirty compressions alternated by twoventilations.

In all three figures, they show from top to bottom:

-   -   the measured infrared raw PPG signal;    -   the high-pass filtered infrared PPG signal;    -   the capnography signal;    -   the electrocardiography (ECG) signal; and    -   the arterial blood pressure (ABP) in the aortic arch.

Before the defibrillation shock (vertical line 300), the animal is incardiac arrest. Cardiac arrest is confirmed by the PPG signal in thisinterval, as it shows a stable oscillating compression signal during thethirty compressions and no oscillations during the pauses forventilations.

After the defibrillation shock, the PPG signal shows presence of anunderlying spontaneous pulse via an increased complexity of thehigh-pass filtered PPG signal during compressions. Return of aspontaneous pulse is also shown by a decrease in the baseline of the PPGsignal. After the defibrillation shock, spontaneous pulses can beobserved in the PPG signal during the pauses for ventilations. Presenceof a spontaneous pulse is confirmed by the increase in arterial bloodpressure (ABP). The ETCO2 level considered in the examples is the one atthe end of the first ventilation following a sequence of thirtycompressions. The relationship between ETCO2 and ABP depends on how wellthe ventilations are controlled.

FIG. 6 shows an example in which the PPG signal shows presence of aspontaneous pulse earlier than ETCO2, i.e. before the ETCO2 levelexceeds the 40 mmHg threshold 302 indicative of ROSC according to theCPR guidelines.

FIG. 7 shows an example in which the PPG signal makes the interpretationof the ETCO2 signal more specific. Already during the cardiac arrestphase before the line 300, the ETCO2 exceeds the 40 mmHg threshold 302indicative of ROSC according to the CPR guidelines. In this interval,however, the PPG signal confirms cardiac arrest. Thus, the PPG signalmakes the interpretation of the ETCO2 signal more specific. The PPGsignal would prevent stopping CPR too early, by showing that aspontaneous pulse is actually absent. After the defibrillation shock,the PPG signal shows presence of a spontaneous pulse by an increasedcomplexity and a decrease in the baseline of the PPG signal. Here asustained rise in ETCO2 only occurs about 90 s after the defibrillationshock, which can be interpreted as an improvement in the perfusion.

FIG. 8 shows an example in which the ETCO2 signal can indicate theadequacy of the perfusion by cardiac contractions. The ETCO2 level doesnot ever exceed the 40 mmHg threshold considered indicative of ROSCaccording to the CPR guidelines. In this example, at about 2020 s,compressions were stopped as ROSC was considered to be achieved.However, the animal collapsed again and CPR had to be reinitiated atabout 2110 s.

In this interval, ETCO2 did not exceed the 40 mmHg threshold indicativeof ROSC according to the CPR guidelines. So here the PPG signal wouldshow that the heart has restarted beating which could withholdvasopressor administration, but the ETCO2 could prevent compressionsfrom being stopped too early.

Thus, combining PPG and ETCO2 has the advantage of maintaining the earlydetection capability of PPG, while obtaining information about perfusionvia ETCO2. Presence of a spontaneous pulse can be detected early viaPPG, which can prevent administration of vasopressors, which can bedetrimental when the heart just resumes cardiogenic output. The ETCO2level can provide a measure of perfusion and thereby show whether thespontaneous circulation can be considered sufficient. When thespontaneous circulation is insufficient according to ETCO2, compressionsshould be continued on a beating heart.

The display outputs shown above in FIGS. 2 to 5 can be supplemented witha capnography signal trace. Additional support for the detection of ROSCis thus enabled by the ETCO2 level, which can provide an indication ofthe level of perfusion.

FIG. 9 shows the system of FIG. 1 enhanced so that the processorreceives inputs from an ECG sensor 400, a CO2 sensor 402 as well as thePPG sensor 102.

The displayed information then includes the fundamental frequencycomponents of the PPG and compression signals, as explained above (as afrequency vs. time plot), but also a set of amplitude vs. time plots,including the ECG and CO2 signals. The raw PPG signal (which includesthe baseline), and high pass filtered PPG signals as shown in FIGS. 6 to8 may also be displayed. Another PPG based signal which may berepresented is the high pass filtered PPG signal from which thecompressions have been removed by further filtering.

Thus signals to present may include:

-   -   an electrocardiography (ECG) signal;    -   one or more photoplethysmography (PPG) based signals (i.e. with        different possible filtering rules, and/or display of        fundamental frequency components only on a frequency axis);    -   a capnography signal (end-tidal CO2, ETCO2);    -   a motion/compression reference signal.

The electrocardiography (ECG) signal may for instance be obtained viathe defibrillation pads as mentioned above. The capnography signal canbe obtained either via a main-stream or a side-stream measurement, froman intubated patient. Non-invasive alternatives also exist for measuringETCO2. Algorithms exist for determining ETCO2 from capnography signals.

In addition to displaying various information as explained above, toenable a clinician to make an assessment, the system may process all ofthe received inputs to generate a single easy to interpret indication ofcardiogenic output.

For example, the PPG and CO2 signals may be interpreted automatically togenerate the following four indications, and they may be color coded onthe display:

No Spontaneous Pulse

In this state, no spontaneous pulse is detected in the PPG signal.Detection of presence of a spontaneous pulse can for instance be done byidentifying the spectral peak corresponding to the spontaneous pulserate. If no spontaneous pulse rate is detected in the PPG spectrum,ETCO2 is not considered further.

Inadequate Spontaneous Pulse

In this state, a spontaneous pulse has been detected in the PPG signal,e.g., by identifying the spectral peak corresponding to the spontaneouspulse rate, but the spontaneous pulse rate is considered to be too low,e.g., below 60/min, to be able to generate a life-sustaining cardiacoutput in these conditions, or the beat-to-beat variation in thespontaneous pulse rate is considered to vary too much over time to beconsidered stable cardiac activity.

In this state, ETCO2 is not considered further.

Stable Spontaneous Pulse with Insufficient Circulation

In this state, a sufficiently high spontaneous pulse rate, e.g., above60/min, has been detected of which the beat-to-beat variation issufficiently small, indicating stable cardiac contractions. However, nosustained increase in ETCO2 has been detected, which exceeds a level of,e.g., 40 mmHg, which is considered to indicate insufficient circulation.

Potential ROSC

In this state, a sufficiently high spontaneous pulse rate, e.g., above60/min, has been detected of which the beat-to-beat variation issufficiently small, indicating stable cardiac contractions. In addition,a sustained increase in ETCO2 has been detected, which exceeds a levelof, e.g., 40 mmHg, which is considered to indicate sufficientcirculation.

When the “Potential ROSC” state is indicated, the clinician can considerinterrupting the chest compressions, to further assess the potentialROSC. In case of an application for lay responders, the algorithm couldprompt for checking the status of the patient in case of the “PotentialROSC” state.

The chest compression measurement (from sensor 104) may also be used. Asexplained above, this helps to discriminate better betweencompression-induced components and spontaneous pulse components in thePPG signal. It also assists in discriminating betweencompression-induced components and ventilation-related components in thecapnography signal to robustly detect the ETCO2 signal. Themotion/compression reference signals can be used as a basis forfiltering to remove components from the PPG and capnography signals.

By using chest compression information, the following fiveidentifications may be derived.

No Spontaneous Pulse

In this state, no spontaneous pulse is detected in the PPG signal.Detection of presence of a spontaneous pulse can for instance be done byidentifying the spectral peak corresponding to the spontaneous pulserate. Furthermore, the ETCO2 signal has not shown any sustained increaseand is below a threshold of, e.g., 40 mmHg.

Spontaneous Pulse Rate≈Compression Rate?

In this state, no spontaneous pulse has been detected in the PPG signalduring ongoing chest compressions, but a sustained increase has beendetected in the ETCO2 level, such that it exceeded a threshold of, e.g.,40 mmHg. This could be indicative of ROSC, with a pulse rate about equalto the compression rate, which explains why no pulse rate was detectedby spectral analysis of the PPG signal. In this situation the cliniciancould consider to shortly interrupt the chest compressions for, e.g., 5s, to determine whether a spontaneous pulse can be observed in the PPGsignal time trace when compressions are stopped.

Inadequate Spontaneous Pulse

In this state, a spontaneous pulse has been detected in the PPG signal,e.g., by identifying the spectral peak corresponding to the spontaneouspulse rate, but the spontaneous pulse rate is considered to be too low,e.g., below 60/min, to be able to generate a life-sustaining cardiacoutput in these conditions, or the beat-to-beat variation in thespontaneous pulse rate is considered to vary too much over time toconsider the cardiac activity to be stable. At the same time, nosustained increase has been detected in ETCO2.

Stable Spontaneous Pulse with Insufficient Circulation

In this state, a sufficiently high spontaneous pulse rate, e.g., above60/min, has been detected of which the beat-to-beat variation issufficiently small, indicating stable cardiac contractions but nosustained increase in ETCO2 has been detected, which exceeds a level of,e.g., 40 mmHg, which is considered to indicate insufficient circulation.

Potential ROSC

In this state, a sufficiently high spontaneous pulse rate has beendetected, e.g., above 60/min, of which the beat-to-beat variation issufficiently small, indicating a stable cardiac contractions and asustained increase in ETCO2 has been detected, which exceeds a level of,e.g., 40 mmHg, which is considered to indicate sufficient circulation.

As explained above, the PPG and capnography signals are analyzed duringongoing compressions. By making use of a reference signal for the chestcompressions, obtained by, e.g., accelerometry, impedance, compressionforce, or radar, the algorithm can distinguish between compressioncomponents and spontaneous pulse components in the PPG signal andbetween compression components and ventilation components in thecapnography signal.

Even more levels of indication may be provided by making use of an ECGsignal as well as the PPG signal, capnography signal and amotion/compression reference signal. In this case, there may be sevendifferent indications:

Cardiac Arrest

In this state, no heart rate is detected in the ECG signal, nospontaneous pulse is detected in the PPG signal, and no sustainedincrease in ETCO2 exceeding a threshold of, e.g., 40 mmHg has beendetected. Detection of heart rate or presence of a spontaneous pulse canfor instance be done by identifying the spectral peak corresponding tothe heart rate and spontaneous pulse rate, respectively.

Heart Rate≈Spontaneous Pulse Rate≈Compression Rate

In this state, no heart rate and no spontaneous pulse rate have beendetected in the ECG and PPG signals during ongoing chest compressions,but a sustained increase has been detected in the ETCO2 level, such thatit exceeded a threshold of, e.g., 40 mmHg. This could be indicative ofROSC, with a heart rate and pulse rate about equal to the compressionrate, which explains why no heart rate and pulse rate were detected byspectral analysis of the ECG and PPG signals. As explained above, inthis situation the clinician could consider to shortly interrupt thechest compressions for, e.g., 5 s, to determine whether the ECG signalis organized and spontaneous pulses can be observed in the PPG signaltime trace when compressions are stopped, and furthermore whether each Rpeak in the ECG signal leads to a pulse in the PPG signal.

Pulseless Electrical Activity

In this state, a heart rate has been measured in the ECG signal, but nopulse has been detected in the PPG signal, and no sustained increase inETCO2 has been detected.

Inconsistent Spontaneous Pulse

A heart rate has been detected in the ECG signal, a pulse rate has beendetected in the PPG signal, but no sustained increase in ETCO2 has beendetected, and the pulse rate is below the heart rate, i.e., not everyR-peak in the ECG signals leads to an actual cardiac contraction.

Consistent but Inadequate Spontaneous Pulse

A heart rate has been detected, a pulse rate has been detected, and theyare equal but the spontaneous pulse rate is considered to be too low,e.g., below 60/min, to be able to generate a life-sustaining cardiacoutput in these conditions, or the beat-to-beat variation in thespontaneous pulse rate is considered to vary too much over time toconsider the cardiac activity stable. At the same time, no sustainedincrease has been detected in ETCO2.

Stable Spontaneous Pulse with Insufficient Circulation

In this case a heart rate and a pulse rate have been detected, and theyare equal. A sufficiently high spontaneous pulse rate, e.g., above60/min, has been detected of which the beat-to-beat variation issufficiently small, indicating stable cardiac contractions. However, nosustained increase in ETCO2 has been detected, which exceeds a level of,e.g., 40 mmHg, which is considered to indicate insufficient circulation.

Potential ROSC

In this state, a heart rate and a pulse rate have been detected, andthey are equal. There is a sufficiently high spontaneous pulse ratedetected, e.g., above 60/min, of which the beat-to-beat variation issufficiently small, indicating stable cardiac contractions. Furthermorea sustained increase in ETCO2 has been detected, which exceeds a levelof, e.g., 40 mmHg, which is considered to indicate sufficientcirculation.

As explained above, when the “Potential ROSC” state is indicated, theclinician can consider interrupting the chest compressions, to furtherassess the potential ROSC.

Displaying frequency vs. time plots as described above enables easydetermination of the pulse rate as well as visual separation of thechest compression components and the pulse rate components. Displayingthe amplitude vs. time waveforms enables beat-to-beat orcompression-to-compression assessment of the signals by the clinicianand allows for the early detection of presence of a spontaneous pulse inthe PPG signal by a decrease in the PPG baseline, and/or an increasedcomplexity of high pass filtered PPG signal and/or appearance of aspontaneous pulse in a PPG signal with the chest compression componentfiltered out.

A simple indicator which outputs one of the indications as explainedabove supports the clinician in interpreting the waveforms.

Instead of or as well as a time history of the compression frequency andpulse frequency, the current values may be displayed numerically, aswell as the current ETCO2 value, and an integral of the CO2 over oneventilation or a series of compressions.

It will be seen from the description above that there are two aspects tothe invention, and they may be combined or used individually. The firstaspect is the extraction of fundamental components of frequency seriespresent in a physiological signal (e.g. PPG) to enable easy detection ofROSC. The second aspect is the combination of a capnography signal and aPPG signal to provide better ease of interpretation. Further additionalsignals may then be combined to provide additional levels ofinterpretation and analysis. The second aspect provides a device forsupporting determination of return of spontaneous circulation, ROSC,during an associated cardiopulmonary resuscitation, CPR, procedure whichis being performed on an associated patient, the device comprising:

-   -   a first input for receiving a first signal from a PPG sensor;    -   a second input for receiving a second signal from a CO2 sensor;    -   a processor, which is adapted to:        -   perform analysis of the first and second signals to provide            an evaluation of whether or not there has been has been a            potential ROSC and provide an output which provides the            evaluation and advised action to a user.

The output may be a displayed indicator. In addition, amplitude vs. timetraces may be provided of the PPG signal and the CO2 signal, as well assignals derived from the PPG signal by filtering, such as a signal withthe PPG baseline removed, the signal with a baseline and a signal withcomponents resulting from CPR compressions filtered out.

The invention is of interest for advanced cardiopulmonary resuscitation(CPR) such for in-hospital CPR as part of a monitor-defibrillator, orfor out-of-hospital CPR by medical professionals. It may be used inadvanced AEDs.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. A single processor or other unit may fulfill thefunctions of several items recited in the claims. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measured cannot be used toadvantage. Any reference signs in the claims should not be construed aslimiting the scope.

1. A device for supporting determination of return of spontaneouscirculation, ROSC, during an associated cardiopulmonary resuscitation,CPR, procedure which is being performed on an associated patient, thedevice comprising: an input for receiving a signal from a sensor forsensing a physiological signal of the patient; a processor, which isadapted to: perform frequency analysis of the physiological signal;detect and discriminate compression-induced components and spontaneouspulse components within the physiological signal; and provide an outputbased on the detected components within the physiological signal tosupport determination that there has been ROSC; and a display device,wherein the processor is adapted to control the display device to outputan image which shows the compression-induced components and spontaneouspulse components within the physiological signal over time as afrequency-time plot.
 2. A device as claimed in claim 1, wherein theprocessor is further adapted to extract the dominant fundamentalfrequency components of harmonic frequency series within thephysiological signal, and to control the display device to output animage based on the extracted dominant fundamental frequency components.3. A device as claimed in claim 2, wherein the processor is adapted toperform frequency analysis of at least the fundamental frequencycomponents and the first harmonic components present in thephysiological signal.
 4. A device as claimed in claim 3, wherein theprocessor is adapted to perform frequency analysis of at least thesecond harmonic components present in the physiological signal.
 5. Adevice as claimed in claim 1, further comprising the sensor for sensinga physiological signal, wherein the sensor comprises an ECG sensor or aPPG sensor.
 6. A device as claimed in claim 5, further comprising afurther sensor or sensors for sensing: the CPR compressions; and/or acapnography signal.
 7. A device as claimed in claim 1, wherein theprocessor is adapted to determine the quality of any determinedpotential ROSC.
 8. A device as claimed in claim 1, wherein the processoris adapted to control the display device to output an image which shows:the quality of the CPR compressions; and/or the quality of anydetermined potential ROSC.
 9. A method for supporting determination ofreturn of spontaneous circulation, ROSC, during an associatedcardiopulmonary resuscitation, CPR, procedure which is being performedon an associated patient, the method comprising: sensing a physiologicalsignal of the patient; performing frequency analysis of thephysiological signal; detecting and discriminating compression-inducedcomponents and spontaneous pulse components within the physiologicalsignal; and providing an output on a display device based on thedetected components within the physiological signal to supportdetermination that there has been ROSC, wherein the ouptut shows thecompression-induced components and spontaneous pulse components withinthe physiological signal over time as a frequency-time plot.
 10. Amethod as claimed in claim 9, comprising extracting the dominantfundamental frequency components of harmonic frequency series within thephysiological signal, and providing an output based on the extracteddominant fundamental frequency components.
 11. A method as claimed inclaim 10, comprising performing frequency analysis of at least thefundamental frequency components and the first harmonic componentspresent in the physiological signal, and optionally also at least thesecond harmonic components present in the physiological signal.
 12. Amethod as claimed in claim 9, wherein the physiological signal comprisesan ECG signal or a PPG signal.
 13. A method as claimed in claim 9,further comprising sensing the CPR compressions and determining thequality of the CPR compressions.
 14. A method as claimed in claim 9,wherein the output shows: the quality of the CPR compressions; and/orthe quality of any determined potential ROSC.
 15. A computer programcomprising computer program code means which is adapted, when run on acomputer, to perform the steps of the method as claimed in claim 9.